Magnetic apparatus



Nov. 1, 1955 R. I. MINCHOM 2,722,636

MAGNETIC APPARATUS I nuenior fiamau- 12am. Mmcmn wiwy A florney Nov. 1, 1955 R. l. MINCHOM MAGNETIC APPARATUS 3 Sheets-Sheet 2 Filed Dec. 7, 1951 Rnounn Isaac rtmcuon Nov. 1, 1955 R. l. MINCHOM 2,722,636

MAGNETIC APPARATUS Filed Dec. 7, 1951 3 Sheets-Sheet 3 Inventor Ram-ms; Isaac Hmcaon United States Patent Ofiice 2,722,636 Patented Nov. 1, 1955 MAGNETIC APPARATUS Raphael Isaac Minchom, Hendon, London, England Application December 7, 1951, Serial No. 260,510

Claims. (Cl. 317-203) This invention relates to magnetic apparatus, particularly, but not exclusively, magnetic apparatus for crack detecting, usually called crack testing apparatus, and has for its object to provide a form of apparatus in which satisfactory contact and transmission of magnetic flux from a magnetised element to another part can be achieved in a manner allowing for considerable variation in the form and contour of the part to which magnetic flux is to be transmitted from the magnetised element.

According to the present invention a magnetic device for leading magnetic flux into a part formed of magnetisable material and/ or for attaching itself magnetically to such a part comprises a holder or support from one face of which project a multiplicity of separate individually movable magnetic flux-carrying contact elements or pins formed of magnetisable material and arranged to slide individually relatively to the support so that their outer ends can be caused to engage surfaces of a wide variety of contours on parts with which they make contact, and a permanent or electro-magnet secured to the support so as to impart magnetic flux to the support and hence to the flux-carrying elements .and through them to any part of magnetisable material with which they make contact.

Preferably the support includes a comparatively thick perforated plate or disc-like part of magnetisable material in the perforations in which lie and can slide the inner ends of the contact pins, the inner ends of the perforations being closed by a magnetic plate to limit the inward movement of the pins while each pin preferably has an enlarged head at its inner .end which makes a close sliding fit with the wall of the perforation in which it lies and moves, and a retaining plate is secured over the outer face of the perforated plate or disc and has perforations through which the shanks of the pins pass freely but through which the heads of the pins cannot pass.

In such an arrangement the head of each pin is preferably conical so as to provide for substantially line contact between its circumference and the wall of the perforation and only substantially point contact :between its end and the plate .closing the inner ends of the perforations, thus limiting friction and tending to prevent the pin being held too firmly in one position by magnetic force.

Such a magnetic device may constitute part of a member which it is desired to attach magnetically to parts of magnetic material, in which case it will be seen that the contact pins can adjust themselves to the contour of the face of the part which they engage by reason of their ability to slide individually.

As stated, the device is particularly applicable to magnetic crack detecting apparatus and in this case crack detecting apparatus according to the invention conveniently includes essentially a holder or support from one face of which project a multiplicity of separate individually movable contact elements or pins formed of magnetisable material and arranged to slide individually relatively to the support so that their outer ends can be caused to engage surfaces of a wide variety of contours on elements or articles to be subject to crack testing, and means whereby the support, and hence the individual contact elements, can be subjected to a magnetic flux which is carried into the article being crack tested by the contact elements.

Preferably in such an arrangement according to the invention the support comprises a relatively thick perforated plate or disc formed of magnetisable material with the inner end portions of individual pin-like contact members sliding in the perforations therein as described above, a high flux permanent or electro-magnet being secured to the back of the perforated plate or to the back of another plate secured to the back of the perforated plate and closing the inner ends of the perforations therein so that when the outer ends of the pins are brought into contact with the surface of an article to be cracktested, magnetic flux is carried from the magnet through the support and pins into such article.

In any case the permanent magnet or electro-magnet is conveniently clamped to the back of the base so as to lie between the rear face of the base and a flux-carrying or concentrating member or element formed of magnetisable material and having a spherical surface thereon for engagement with spherical surfaces on other flux-carrying elements capable of forming in effect a flexible flux-carrying path. Thus, while in some cases it will be found that the magnetic field generated by the magnet is sufficiently powerful to enable crack testing of parts or articles of highly magnetisable materials to be satisfactorily effected simply by bringing the contact elements or pins of a single support into engagement with an appropriate part of the part of articles to be crack tested, it will generally be found desirable or necessary to provide ,a flexible magnetic flux path enabling additional magnetic flux to be led through the part to be crack tested.

Magnetic crack testing apparatus according to the invention will therefore preferably comprise two supports according to the invention with their contact elements each having a magnet attached thereto in the manner referred to above but with the magnetic poles of the two magnets oppositely disposed in relation to their associated supports so that the two supports can be applied to opposite sides or ends of the article or part to be crack tested with their contact elements in engagement with the appropriate surfaces of such article or part and with intermediate fluxcarrying members arranged to extend between the two supports and formed and arranged to constitute a flexible closed flux path outside the part to be crack tested and extending between the bases of the two supports when the latter are applied to the different points on the part to be crack tested.

One construction of crack testing apparatus of this kind according to the invention and certain modifications thereof are illustrated by way of example in the accompanying drawings, in which Figure 1 is a view showing the various separate assemblies constituting one form of crack testing apparatus according to the invention,

Figure 2 shows the crack testing apparatus illustrated in Figure 1 with the various assemblies combined,

Figure 3 is a perspective view, partly in section, on an enlarged scale showing the internal construction of one of the parts by which magnetic flux is carried into an article to be crack tested,

Figure 4 is an end view of the part shown in Figure 3,

Figure 5 is a side elevation, partly in section, showing a detailed construction of the apparatus shown in Figures 1 to 4,

Figure 6 indicates how, by increasing the number of elements used, the flexibility of crack testing apparatus according to the invention can be increased,

Figure 7 shows a modification of the invention enabling remagnetisation to be readily achieved when desired, and

Figure 8 shows a further modification.

In the arrangement shown in Figures 1, 2, 3, 4, and the apparatus comprises two assemblies (hereinafter called heads) for carrying magnetic flux respectively to spaced points on a part or article to be crack tested, and three additional assemblies which can be assembled with the heads as to form in effect a flux-carrying path between them.

Each of the heads comprises a cylindrical block in the form of a thick plate A of magnetisable material having formed therein a series of parallel bores A a back plate A also of magnetisable material which is secured to the plate A by screws A so as to close the inner ends of the bores, and a front plate A of brass or other non-magnetic material having holes A therein which register with, but are of slightly smaller diameter than the bores A this plate A being secured to the plate A by screws A Arranged to slide through the holes in the plate A and within the bores A are pins B each of which has a conical enlarged head B which constitutes a stop to prevent the pin being withdrawn completely from its bore through the plate A the conical form of the heads B ensuring that when the pins lie in their innermost positions they make only limited contact with the base plate A The base plate A is rigidly clamped to one end of a cylindrical permanent magnet C by a central screw C which passes axially through the magnet and serves also to clamp to the other end of the magnet 21 ball member D formed with a flat thereon so as to pro vide as large an area of contact between the magnet and the ball member as possible. The ball member D is formed of readily magnetisable material.

If desired the parts C, A, and A may be enclosed within a cover of non-magnetic metal or other material to prevent direct contact of these parts with adequate parts during use of the device.

Formed for attachment to each of the ball members D is an intermediate flux-carrying element comprising a cylindrical bar E of readily magnetisable material having a concave spherical surface E at one end for engage ment with the spherical surface of its associated ball member D, and a spring clip device F having three spring fingers which can embrace the ball member to prevent unintentional disengagement of the ball member from the end of the bar E. As shown, the clip device F comprises a split collar portion which surrounds the adjacent end of the bar E and has two or more fingers F lying in a circumferential groove in this bar and three spring fingers F which embrace the ball member D. Secured by a screw-threaded member G to the opposite end of each bar E is a ball member H of readily magnetisable material. The clip device F, F is preferably formed of non-magnetic material and may have any convenient number of fingers.

An intermediate member is provided for connecting magnetically the two ball members H, this intermediate member comprising a central part including a cylindrical magnet J and two cylindrical parts I of magnetisable material clamped thereto by a screw J the whole being enclosed in a non-magnetic sheath J of rubber or the like, the outer ends of the parts J being provided with concave spherical surfaces J for engagement with the ball members H and also carrying spring clip devices F similar to the devices F on the parts E for preventing unintentional disengagement of the ball members H from the surfaces J Whereas the ball member D of one of the heads is clamped to the north pole end of its magnet C, the ball member D of the other head is clamped to the south pole end of its magnet C, while in use the magnet J is disposed so that when the apparatus is in use as shown in Figure 2 its magnetic flux serves to increase the magnetic flux in the magnetic circuit as a whole which is produced when the various elements are assembled as shown in Figure 2,

It will be understood that if desired the parts E may also be formed as or include magnets arranged further to increase the magnetic flux in the magnetic circuit as a whole when the parts are assembled as shown in Figure 2.

When the apparatus is in use as shown in Figure 2 it will be seen that the pins B serve to transmit magnetic flux to the article, indicated at K, to be crack tested and that by reason of their ability to slide individually they can perform this function satisfactorily in respect of articles having a variety of external contours.

As will be seen from Figure 6, the number of intermediate flux-carrying elements used between the two heads in crack testing apparatus according to the invention can be increased above the minimum shown in Figures 1 and 2 by the addition of further elements similar to the elements E, E, H shown in Figure 1 with or without magnets incorporated in such elements.

In the modification shown in Figure 7 the apparatus is similar to that shown in Figures 1 and 2 except that instead of or in addition to the cover 1 a coil of conducting wire J is wound around the element comprising the parts I, I J and is provided with electrical terminals as indicated at 1 With this arrangement, by arranging. the apparatus in the position shown so as to provide a closed magnetic circuit and then connecting the terminals J to the appropriate terminals of an electric battery, for example a 6- or 12-volt battery of the kind normally used on automobiles, for a period of a few seconds the magnets comprised in the apparatus can be remagnetised should their magnetic flux become reduced in use.

It will be appreciated that it is essential that the north and south poles of the various magnets in the apparatus should be correctly positioned, and to this end each of the elements including a magnet will preferably be appropriately marked with the letters N and S at its two appropriate ends either alone or in association with other marking, while similarly the terminals J will be appropriately marked so as to be sure that the parts will be correctly placed and the terminals correctly connected to achieve the desired remagnetisation.

In the modification shown in Figure 8, a short connecting piece L of magnetic material is provided with part spherical surfaces L for engagement with the ball members D in the manner indicated to facilitate crack testing of parts such as that indicated at M in some cases.

It is to be understood that although the invention has been described with particular reference to constructions using permanent magnets, devices according to the invention may instead or in addition incorporate one or more electromagnets with suitable means for connecting their energising coils to a source of electric supply. For example, apparatus as shown in Figure 7 might be provided either including permanent magnets or merely unmagnetised flux carrying elements, and the coil 1 then connected to a suitable battery to provide or enforce the magnetic flux when the apparatus is to be used.

It will be appreciated that in using crack testing apparatus according to the invention the part to be crack tested will have magnetic ink of the usual kind applied to it so as to render cracks readily visible under the action of the magnetic flux applied to the part by the apparatus.

What I claim as my invention and desire to secure by Letters Patent is:

l. A magnetic device for leading magnetic flux into a part formed of magnetizable material and for attaching itself thereto comprising a magnetic head formed of magnetizable material, a multiplicity of individually movable flux-carrying contact pins, formed at least in part of magnetizable material, which pins project from one face of the magnetic head and lie at least partly within recesses formed in the magnetic head, and are freely slidable parallel to one another in one direction under the influence of the magnetic flux they carry and are spaced in two directions at right angles to this direction of movement, so that their outer ends may engage surfaces of a variety of contours on parts with which they make contact, the magnetizable parts of the contact pins being out of contact with one another but arranged closely adjacent to the magnetic head to receive magnetic flux directly therefrom, and a magnet secured to the magnetic head so as to impart magnetic flux to the magnetic head and hence to the flux carrying contact pins and through them to any part of magnetizable material with which they make contact.

2. A magnetic device for leading magnetic flux into a part formed of magnetisable material as claimed in claim 1 in which the magnetic head comprises a comparatively thick perforated disc-like part of magnetisable material in the perforations in which lie and can slide the inner ends of the contact pins, the inner ends of the perforations being closed to limit the inward movement of the pins, while each pin has an enlarged head at its inner end which thus lies closely adjacent to the wall of the perforation in which it lies and moves, and a retaining disc of non-magnetizable material secured to the outer face of the thick perforated disc, and having perforations through which the shanks of the pins pass freely but through which the heads of the pins cannot pass.

3. A magnetic device as claimed in claim 1 in which the inner ends of the recesses are closed by a part of magnetizable material and in which the inner end of each contact pin is formed with a point extending towards the closed end of the recess in which the pin lies.

4. Magnetic apparatus for crack testing as claimed in claim 5, including a magnet disposed between the rear face or base of each magnetic head and a flux carrying element of magnetisable material having a spherical surface thereon for engagement with a spherical surface on other flux-carrying elements formed of magnetisable material.

5. Magnetic apparatus for crack-testing including two magnetic heads formed at least in part of magnetizable material, a multiplicity of individually movable flux carrying contact pins formed at least in part of magnetizable material which project from one face of each magnetic head and lie at least partly within recesses in the magnetic heads and are freely slidable in one direction parallel to one another under the influence of the magnetic flux they carry, and are spaced in two directions at right angles to this direction of movement, so that their outer ends may engage surfaces of a variety of contours on parts with which they make contact, the magnetizable parts of the contact pins being out of contact with one another but arranged closely adjacent to the magnetizable parts of the magnetic heads to receive magnetic flux directly therefrom, and means for imparting magnetic flux to the magnetic heads and hence to the flux-carrying contact pins and through them to any part of magnetizable material with which they make contact.

6. Magnetic apparatus for crack-testing as claimed in claim 5 in which each magnetic head comprises a mass of magnetizable material provided with parallel bores in which lie the inner ends of the contact pins, the inner ends of the bores being closed to limit the inward movement of the pins, while each pin has an enlarged head on its inner end which thus lies closely adjacent to the wall of the bore in which it lies to receive magnetic flux directly therefrom, and is formed with a point extending towards the closed end of the bore, and a locating member of non-magnetizable material secured to the magnetic head and having apertures through which the shanks of the pins pass freely but through which the heads of the pins cannot pass.

7. Magnetic apparatus for crack testing as claimed in claim 4, including flux-carrying elements formed to constitute a flexible closed flux-carrying path between the backs of the two magnetic heads when the latter are applied to different points on a part to be crack tested.

8. Magnetic apparatus for crack testing as claimed in claim 7 in which the end of each magnet remote from its associated magnetic head is rigidly connected to a flux-carrying member having an exposed spherical surface, and a plurality of intermediate flux-carrying elements are provided each having at its ends exposed spherical surfaces such that the intermediate flux-carrying elements can be arranged end to end in a series or chain between the flux-carrying members with the appropriate co-operating convex or concave end spherical surfaces in close contact.

9. Magnetic apparatus for crack testing as claimed in claim 8, including resilient devices for preventing unintentional disengagement from one another of the various engaging spherical surfaces.

10. Magnetic apparatus for crack testing as claimed in claim 9, in which at least one of the intermediate flux carrying elements itself includes a permanent magnet by which the magnetic flux in the assembly as a whole is increased.

11. Magnetic apparatus for crack testing including two contact members each comprising a magnetic head and a multiplicity of flux carrying contact pins as claimed in claim 1, a part having a spherical surface rigid with each support, a plurality of intermediate flux-carrying elements having interengaging spherical surfaces forming a closed flux carrying path between the backs of the two supports when the latter are applied to different points on a part to be crack tested, and means for applying a magnetic flux to said closed flux-carrying path.

12. Magnetic apparatus for crack testing as claimed in claim 11, in which the means for applying magnetic flux comprises one or more permanent magnets incorporated in each of the contact members.

13. Magnetic apparatus for crack testing as claimed in claim 12 including at least one additional permanent magnet incorporated in one of the elements constituting the closed flux-carrying path between the backs of the contact members.

14. Magnetic apparatus for crack testing as claimed in claim 11, in which the means for applying magnetic flux to the closed flux carrying path includes permanent magnets on each of the contact members and in which at least one element of the flux-carrying path includes an electrical winding and terminals by which the Winding can be energised to apply additional magnetic flux to the flux-carrying path.

15. Magnetic apparatus for crack testing as claimed in claim 13, in which the means for applying magnetic flux to the flux-carrying path includes at least one electrical winding upon an element of the flux-carrying path with appropriate terminals for connecting it to a source of direct current.

References Cited in the file of this patent UNITED STATES "PATENTS 435,343 Brown Aug. 26, 1890 2,225,179 Oglevee Dec. 17, 1940 2,242,220 Barnes et al. May 20, 1941 2,318,923 Clark May 11, 1943 2,476,943 Brady July 19, 1949 2,575,811 Hofammann et al. Nov. 20, 1951 

